Updated on May 8, 2023
There are a wide range of indoor pests out there that can cause a panic. Roaches and termites can be serious threats, but may not pose a direct health risk. On the other hand, bed bugs, fleas, and lice are three that actively drink blood and pose a different kind of threat.
Of these three, fleas are perhaps the most misunderstood. They’re also the most dangerous. Because of how often fleas are mistaken for other critters, it’s important to know how to identify them, as well as knowing the difference between some of the most common species.
How to Spot Fleas
Usually the first sign of fleas (besides your pet scratching itself) is a tiny, seemingly black speck suddenly leaping a foot into the air or skittering through your pet’s fur. However, there are other ways to spot a flea, as well as identify which type of flea they are.
Yes, you heard right – there are more than 2,500 species of flea out there, with more than 300 found in the US.
See Also: Will Rubbing Alcohol Kill Fleas Instantly?
Are Fleas Visible to the Human Eye?
Fleas are very small but not too small to see. The eggs look like tiny specks of white grit or sugar while the adults are a dark reddish-brown that often appears almost black unless they’ve recently had a blood meal. A dead flea on its side will look like a small, flat seed with tiny hairs (actually their long legs) coming off of one end.
You can also spot flea activity by their frass (commonly known as flea dirt), which looks like tiny black grit and will turn into a red stain if you touch it with a damp paper towel. Flea dirt is actually dried blood remains. When left near flea eggs, it can look like someone seasoned your pet’s fur with salt and pepper.
How Big Do Fleas Get?
An adult flea is around 1/8 inches long, which is a little over twice the size of a sesame seed. This is pretty much the same for all species you’re likely to run into.
How Different Types of Fleas Look
We’ll be honest here: You’re going to need a very good magnifying glass or a basic microscope and a dead specimen to really be able to identify one species from another. Sometimes it’s hard enough identifying a flea vs another bug.
However, there are some basic differences you can use to narrow down the species a little bit, including the animals they prefer to infest.
#1 – Cat Fleas (Ctenocephalides felis)
Chances are, if you’ve done a search for fleas, this is the one pictured. That’s because this species (which has several subspecies) is the most common flea in the world.
Originating in Africa, the cat flea became cosmopolitan as feline domestication became more widespread. However, cat fleas don’t affect just cats, they also can infest dogs and other pets as well.
When separated from the host, male cat fleas will die in two days, females in three. Only 5 percent of an infestation are adults, and cat fleas are highly resistant to pesticides due to overuse.
Signs Your Cat Has Fleas
The most common symptom of a flea problem is abnormally frequent scratching. This can result in sores or bald patches where the cat had frequently scratched, which encourages the fleas to feed there, which in turn causes additional itching.
You may also notice black or white “grit” when brushing your cat or fingering through its fur. In extreme cases, your cat will suffer an allergic reaction to one of 15 substances in flea saliva, or become anemic due to blood loss from a particularly heavy infestation.
See Also: How to Treat Flea Bites on Kids
Disease Risks
Cats with fleas (especially strays) carry a range of several diseases and are suspected to be vectors between humans and other animals. Bartonella and murine typhus (a flea-born version of typhoid) are both common pathogens, as well as the tapeworm species Dipylidium caninum (which can infect humans and animals if the flea is swallowed).
Less commonly, cat fleas can pass on Borrelia burgdorferi (one of the bacteria that can cause Lyme disease) and Rickettsia felis. While rare, Yersinia pestis – the bacteria that causes bubonic plague – can also be carried by cat fleas.
#2 – Dog Fleas (Ctenocephalides canis)
A close relative of cat fleas in appearance and… tastes, the dog flea primarily affects dogs with a close secondary preference for cats. Much like the cat flea, dog fleas will attack other animals when the primary hosts aren’t available, including humans.
There are two visible differences between the species, however. Dog fleas have more rounded heads while cat fleas are more elongated, and dog fleas have two additional notches in their hind legs.
Signs Your Dog Has Fleas
Similar to cats, dogs will have an abnormal level of scratching, especially around the head, neck, and tail regions. This can result in skin irritation, bald patches, or other symptoms associated with frequent scratching.
While more rare than in cats, infested dogs can become anemic, and tapeworms are a common side effect.
Disease Risks
While not a common pest in the US, an infestation can still pose some risk. The most common problem caused by dog fleas is the transmission of Dipylidium caninum.
Read Also: Do Fleas Drown in Water?
#3 – Human Fleas (Pulex irritans)
We wouldn’t be surprised if you’ve never heard of this species. It was originally referred to as the house flea and is believed to have originated in South America.
This flea will infest a wide range of hosts, including humans, and can be identified by a rounded head and a more horizontal back than many other species.
Disease Risks
There’s only one significant disease risk from this species, which is Yersinia pestis. However, the risk is fairly low compared to the rat flea.
#4 – Rat Fleas (Xenopsylla cheopis)
There are three major species of rat flea, two of which can be found in the US: the northern rat flea (Nosopsyllus fasciatus) and Oriental rat flea (Xenopsylla cheopis).
These two species can be difficult to distinguish from other types of flea and are best known by the number of spines (northern) or lack of spines (Oriental). As the name suggests, they mostly infest rats and mice, with the northern species preferring domestic breeds.
Disease Risks
If you’ve ever heard of the bubonic plague, Yersinia pestis should send off alarms. In fact, the rat flea was the primary vector of this disease, and efforts to kill cats resulted in a rat population explosion. This, in turn, led to a massive rat flea infestation across Europe with the primary rat predator no longer readily available.
Bats, which were also blamed for the plague, are now believed to have been possibly infested with rat fleas or otherwise guilty because they resemble flying rats.
#5 – Chicken Fleas (Ceratophyllus gallinae)
These peculiar fleas have a long, flat back and only infest birds. However, they’re easily distinguished by the way they stick vertically from the bite area, making them look more like blackheads at first.
They can cause anemia and other issues related with blood loss but are not considered a significant disease vector.
#6 – Sand Fleas (Tunga penetrans)
There are a number of critters that get the nickname of sand flea, but these are the real deal. Unlike the other fleas we’ve discussed, sand fleas like to burrow into the host’s skin where they feed and lay their eggs.
Getting sand fleas is nasty business, but thankfully they’re not found in the US outside of the Caribbean territories.
A Brief Flea FAQ
To finish off, here are a few common questions regarding fleas and identification.
Is It Possible to Have Fleas and Not See Them?
This is a more common occurrence than one might think. Only a tiny percentage of a flea infestation are adults, so it’s easy to have an infestation and not notice it for some time.
Can There Be Fleas in My Home if I Don’t Have a Pet?
Depending on the species, a flea in its pupal stage can hibernate up to two years without food. Carbon dioxide and other environmental signals will tell the pupa that food is near, causing the adult to emerge.
Additionally, fleas are known to migrate indoors through entry points if they lack a host. You can also sometimes bring fleas home if you were inclose contact with an infested pet or its bedding.
What Do Flea Eggs Look Like?
Flea eggs are tiny white ovals that tend to resemble grains of sugar until placed under a magnifying glass.
Can Fleas Live on Humans or in Their Hair?
Despite what some sources might tell you, some species of fleas can actually live on humans. The human flea mentioned above can infest the hair, eyebrows, armpits (if unshaved) and pubic region.
Cat fleas and other species can survive on humans in a pinch, but they much prefer other animals and usually won’t remain on humans once a better food source appears.
Note that this is one of the few occasions in which a flea will “jump ship”. In most cases, a flea prefers to remain on its host for its entire life.
Morgan is a certified entomologist and pest control consultant and a member of the National Pest Management Association.
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